Abstract
Abstract. The Gauss–Seidel limb scattering (GSLS) radiative transfer (RT) model simulates the transfer of solar radiation through the atmosphere and is imbedded in the retrieval algorithm used to process data from the Ozone Mapping and Profiler Suite (OMPS) limb profiler (LP), which was launched on the Suomi NPP satellite in October 2011. A previous version of this model has been compared with several other limb scattering RT models in previous studies, including Siro, MCC++, CDIPI, LIMBTRAN, SASKTRAN, VECTOR, and McSCIA. To address deficiencies in the GSLS radiance calculations revealed in earlier comparisons, several recent changes have been added that improve the accuracy and flexibility of the GSLS model, including 1. improved treatment of the variation of the extinction coefficient with altitude, both within atmospheric layers and above the nominal top of the atmosphere; 2. addition of multiple-scattering source function calculations at multiple solar zenith angles along the line of sight (LOS); 3. introduction of variable surface properties along the limb LOS, with minimal effort required to add variable atmospheric properties along the LOS as well; 4. addition of the ability to model multiple aerosol types within the model atmosphere. The model improvements 1 and 2 are verified by comparison to previously published results (using standard radiance tables whenever possible), demonstrating significant improvement in cases for which previous versions of the GSLS model performed poorly. The single-scattered radiance errors that were as high as 4% in earlier studies are now generally reduced to 0.3%, while total radiance errors generally decline from 10% to 1–3%. In all cases, the tangent height dependence of the GSLS radiance error is greatly reduced.
Highlights
Incoming solar irradiance interacts with the Earth’s atmosphere as it penetrates downwards towards the surface
These retrieval algorithms have shown a remarkable degree of accuracy despite the shortcomings of the Gauss–Seidel limb scattering (GSLS) model, but development of a more accurate version of the GSLS model is desirable for the purpose of interpreting residuals
The GSLS radiative transfer (RT) model has been updated relative to the L04 version, significantly improving the calculated limb scattered radiances
Summary
Incoming solar irradiance interacts with the Earth’s atmosphere as it penetrates downwards towards the surface. The multiple-scattering (MS) source function is calculated at one or more points along the LOS using the pseudo-spherical version of the RT model described by Herman et al (1994, 1995). The GSLS model has been used for retrieval applications on missions including SOLSE/LORE (Flittner et al, 2000), SAGE III (Rault, 2005; Rault and Taha, 2007), GOMOS (Taha et al, 2008), SCIAMACHY (Taha et al, 2011) and OMPS LP (Rault and Loughman, 2013) These retrieval algorithms have shown a remarkable degree of accuracy despite the shortcomings of the GSLS model, but development of a more accurate version of the GSLS model is desirable for the purpose of interpreting residuals (differences between measured radiances and radiances calculated for the desired model atmosphere). For more comprehensive information concerning the OMPS LP sensor, consult Flynn et al (2006), Rault and Loughman (2013), and Jaross et al (2014)
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